The vergence eye movement system is responsible for the normal alignment of the visual axes. Although misalignment of the eyes is a common human oculomotor disorder, the neurophysiology of the vergence system has received little experimental attention. The proposed project is a comprehensive examination of the neural substrates of the vergence system using electrophysiological and anatomical techniques. Monkeys will be trained to make precise saccadic, smooth pursuit, and vergence movements on demand. The position of each eye in the orbit will be measured using the very accurate electromagnetic search coil technique. Brain areas in and around the abducens and oculomotor nuclei, as well as the superior colliculus, pretectum and areas in the underlying mesencephalic tegmentum will be studied using single unit and electrical microstimulation techniques. The 14C-2-deoxyglucose autoradiographic technique will be used in trained monkeys to select specific brain areas for further study. The goals of this research are 1) to determine the site(s) at which vergence and versional signals are combined and discover the form of the vergence signal; 2) to explore areas in or around the oculomotor complex which may mediate a vergence signal; and 3) to discover sites in the midbrain through which vergence commands originating in the neocortex may be relayed to oculomotor areas.